Interesting article regarding time and rate of skeletal maturation in horses
Excerpt from Dr. Deb Bennett's paper:
All Horses of All Breeds Mature Skeletally at the Same Rate
(ABOUT Dr. Bennett, Ph.D., is a 1984 graduate of the University of Kansas, and until 1992 was with the Smithsonian Institution. She is known as an authority on the classification, evolution, anatomy, and biomechanics of fossil and living horses.)
...Let me repeat that: no horse on earth, of any breed, at any time, is or has ever been mature before the age of six (plus or minus six months). So, for example, the Quarter Horse is not an "early maturing" breed - and neither is the Arabian a "slow maturing" breed. As far as their skeletons go, they are the same. This information comes, I know, as a shock to many people who think starting their colt or filly under saddle at age two is what they ought to be doing. This begs discussion of (1) what I mean by "mature" and (2) what I mean by "starting".
When is a Horse Skeletally Mature?
Just about everybody has heard of the horse's "growth plates", and commonly when I ask them, people tell me that the "growth plates" are somewhere around the horse's knees (actually the ones people mean are located at the bottom of the radius-ulna bone just above the knee). This is what gives
rise to the saying that, before riding the horse, it's best to wait "until his knees close" (i.e., until the growth plates convert from cartilage to bone, fusing the epiphysis or bone-end to the diaphysis or bone-shaft). What people often don't realize is that there is a "growth plate" on either end of every bone behind the skull, and in the case of some bones (like the
pelvis, which has many "corners") there are multiple growth plates.
So do you then have to wait until all these growth plates convert to bone? No. But the longer you wait, the safer you'll be. Owners and trainers need to realize there's a definite, easy-to-remember schedule of fusion and then make their decision as to when to ride the horse based on that rather
than on the external appearance of the horse. For there are some breeds of horse the Quarter Horse is the premier among these which have been bred in such a manner as to look mature long before they actually are mature. This puts these horses in jeopardy from people who are either ignorant of
the closure schedule, or more interested in their own schedule (for futurities or other competition) than they are in the welfare of the animal.
The Schedule of Growth-Plate Conversion to Bone
The process of converting the growth plates to bone goes from the bottom of the animal up. In other words, the lower down toward the hoofs you look, the earlier the growth plates will have fused; and the higher up toward the animal's back you look, the later. The growth plate at the top of the
coffin bone (the most distal bone of the limb) is fused at birth. What that means is that the coffin bones get no taller after birth (they get much larger around, though, by another mechanism). That's the first one. In order after that:
* Short pastern - top and bottom between birth and 6 months.
* Long pastern - top and bottom between 6 months and one year.
* Cannon bone - top and bottom between 8 months and 1.5 years
* Small bones of the knee - top and bottom of each, between 1.5 and
* Bottom of radius-ulna - between 2 and 2.5 years
* Weight-bearing portion of glenoid notch at top of radius - between
2.5 and 3 years
* Humerus - top and bottom, between 3 and 3.5 years
* Scapula - glenoid or bottom (weight-bearing) portion – between 3.5
and 4 years
* Hindlimb - lower portions same as forelimb
* Hock - this joint is "late" for as low down as it is; growth plates on the tibial and fibular tarsals don't fuse until the animal is four (so the hocks are a known "weak point" - even the 18th-century literature warns against driving young horses in plow or other deep or sticky footing, or jumping them up into a heavy load, for danger of spraining their hocks).
* Tibia - top and bottom, between 3 and 3.5 years
* Femur - bottom, between 3 and 3.5 years; neck, between 2.5 and 3 years; major and 3rd trochanters, between 2.5 and 3 years
* Pelvis - growth plates on the points of hip, peak of croup (tubera sacrale), and points of buttock (tuber ischii), between 3 and 4 years.
And what do you think is last? The vertebral column, of course. A normal horse has 32 vertebrae between the back of the skull and the root of the dock, and there are several growth plates on each one, the most important of which is the one capping the centrum. These do not fuse until the horse is at least 5 ½ years old (and this figure applies to a small-sized, scrubby, range-raised mare. The taller your horse and the longer its neck, the later the last fusions will occur. And for a male - is this a surprise? - you add six months. So, for example, a 17-hand Thoroughbred or Saddlebred
or Warmblood gelding may not be fully mature until his 8th year - something that owners of such individuals have often told me that they "suspected"). Significance of the Closure Schedule for Injuries to Back and Neck vs. Limbs
The lateness of vertebral "closure" is most significant for two reasons. One: in no limb are there 32 growth plates! Two: the growth plates in thelimbs are (more or less) oriented perpendicular to the stress of the load passing through them, while those of the vertebral chain are oriented parallel to weight placed upon the horse's back. Bottom line: you can
sprain a horse's back (i.e. displace the vertebral physes) a lot more easily than you can displace those located in the limbs.
Here's another little fact: within the chain of vertebrae, the last to fully close" are those at the base of the animal's neck (that's why the long-necked individual may go past 6 years to achieve full maturity - it's the base of his neck that is still growing). So you have to be careful - very careful - not to yank the neck around on your young horse, or get him
in any situation where he strains his neck (i.e., better learn how to get a horse broke to tie before you ever tie him up, so that there will be no likelihood of him ever pulling back hard. ).
What Does it Mean to "Start" a Young Horse?
Let us now turn to the second discussion, which is what I mean by "starting" and the whole history of that. Many people today - at least in our privileged country - do not realize how hard you can actually work a mature horse - which is very, very hard. But before you can do that without
significantly damaging the animal, you have to wait for him to mature, which means - waiting until he is four to six years old before asking him to carry you on his back.
What bad will happen if you put him to work as a riding horse before that? Two important things - and probably not what you're thinking of. What is very unlikely to happen is that you'll damage the growth plates in his legs. At the worst, there may be some crushing of the cartilages, but the
number of cases of deformed limbs due to early use is tiny. The cutting-horse futurity people, who are big into riding horses as young as a year and a half, will tell you this and they are quite correct. Want to damage legs? There's a much better way - just overfeed your livestock (you ought to be able to see a young horse's ribs - not skeletal, but see 'em -
until he's two).
Structural damage to the horse's back from early riding is somewhat easier to produce than structural damage to his legs. There are some bloodlines (in Standardbreds, Arabians, and American Saddlebreds) that are known to inherit weak deep intervertebral ligament sheathing; these animals are
especially prone to the early, sudden onset of "saddle back'" However, individuals belonging to these bloodlines are by no means the only ones who may have their back "slip" and that's because, as mentioned above, the stress of weightbearing on the back passes parallel to its growth plates as well as parallel to the intervertebral joints. However, I want to add that the frequency of slipped backs in horses under 6 years old is also very low.
So, what's to worry about? Well...did you ever wish your horse would "round up" a little better? Collect a little better? Respond to your leg by raising his back, coiling his loins, and getting his hindquarter up underneath him a little better? The young horse knows, by feel and by "instinct", that having a weight on his back puts him in physical jeopardy. I'm sure that all of you start your youngstock in the most humane and
considerate way that you know how, and just because of that, I assure you that after a little while, your horse knows exactly what that saddle is and what that situation where you go to mount him means. And he loves you, and he is wiser than you are, so he allows this. But he does not allow it
foolishly, against his deepest nature, which amounts to a command from the Creator that he must survive; so when your foot goes in that stirrup, he takes measures to protect himself.
The measures he takes are the same ones you would take in anticipation of a load coming onto your back: he stiffens or braces the muscles of his topline, and to help himself do that he may also brace his legs and hold his breath ("brace" his diaphragm). The earlier you choose to ride your horse, the more the animal will do this, and the more often you ride him
young, the more you reinforce the necessity of him responding to you in this way. So please - don't come crying to me when your six-year-old (that you started under saddle as a two year old) proves difficult to round up. Any horse that does not know how to move with his back muscles in release cannot round up.
Bottom line: if you are one of those who equates "starting" with "riding", then I guess you better not start your horse until he's four. That would be the old, traditional, worldwide view: introduce the horse to equipment (all kinds of equipment and situations) when he's two, crawl on and off of him at three, saddle him to begin riding him and teaching him to guide at four, start teaching him maneuvers or the basics of whatever job he's going to do - cavalletti or stops or something beyond trailing cattle - at five, and he's on the payroll at six. The old Spanish way of bitting reflected this
also, because the horse's teeth aren't mature (the tushes haven't come in, nor all of the permanent cheek teeth either) until he's six."
Nothing with horses is ever easy or cheap. And if it is, you're doing it wrong. They always rip out part of your soul when they leave. I guess that's how they find us later.
So why if the back doesn't physically mature at 6 is there even information for going ahead at 4? FWIW, I don't equate starting with riding. Didn't even start jumping my mare til this year at 5. Yeah she did small things younger but to me she wasn't physically or mentally mature enough to handle anything else. And has had 2 months off here recently as a 5 YO. But I can't be an advocate for starting and riding at 6.
COTH, keeping popcorn growers in business for years.
"I need your grace to remind me to find my own." Snow Patrol-Chasing Cars. This line reminds me why I have horses.